confused about the function "point_triangle_distance"

[shoujieqiu]

I want to konw where I can find the theory/proof about this function?Thank a lot!

[shoujieqiu]

I'm sorry my question is not specific enough.Could you teach me in the function point_triangle_distance
float invdet=1.f/max(m13m23-dd,1e-30f);
why shall we do so?

[YuDe95]

do you find the theory/proof about this function?i only konw it's about Barycentric Coordinates